I am setting up a smoke system on a 60 sixty size plane with a OS91FX the plane is not ready to fly yet. But tapping into the back plate of the crank case on a 2 stroke and using that pressure is the best way to go also wrapping some tubing around the head or muffler to preheat the smoke oil makes a big difference. A 4 stroke requires a pump to get the smoke oil to the exhaust. It is much more complicated and heaver. You may find it increases your wing loading to the point that you loose performance. That is why I am putting mine on a sixty size plane and not any thing smaller.